I noticed that your first sketch is not constrained or making use of symmetry about the origin.
You might want to read this document http://home.pct.edu/~jmather/skillsusa%20university.pdf
You don't need all of those workplanes for the split it can be done with a single sketch (like attached image or some variation).
I would probably split faces (not part) and then Derive Component in another file and Thicken panels as needed (do one, Save As, undo, do next until all finished).
Don't forget to set the sheet metal thickness in the derived.